Radio over fiber (RoF) refers to a technology whereby Radio Frequency (RF) signals are modulated on an optical carrier and transmitted over an optical fiber link. In other words, radio signals are carried over fiber-optic cable. The RF signals may be wireless RF signals.
With RoF technology an optical network may be used to federate several radio antennas thanks to the large bandwidth offered by the optical fiber link and its low loss. RoF may be deployed in many modern radio systems, such as 3rd Generation Partnership Project (3GPP) Universal Mobile Telecommunications System (UMTS) or 3GPP Long Term Evolution (LTE).
A fronthaul link is the link between a base station baseband unit or base station digital unit to a remote radio head and antenna. In other words, the fronthaul link is the link between the baseband or digital unit of a base station, usually in a centralized location, to a remote radio head and antenna. RoF may reduce latency and simplify radio head complexity, e.g. by moving Analogue-to-Digital Converters (ADC) and Digital-to-Analogue Converters (DAC) closer to the baseband unit, in fronthaul.
However, RoF in fronthaul suffers from cumulative effects of noise and nonlinearities of optical devices as well as crosstalk arising from impairments in the optical fiber link.
Within a point-to-point fiber link connecting the remote radio head and antenna and a central office, comprising the baseband unit, received wireless RF signals undergo electrical-to-optical conversion via a directly modulated laser or an external modulation, e.g. using an electro-optic modulator in conjunction with an optical carrier.
As a drawback, in RoF, the overall system performance of the optical network is limited by the performance of the optical subsystems of the optical network, such as the directly modulated laser. This is primarily due to a nonlinear transfer function of the electro-optical modulator or the directly modulated laser used in the transceiver.